Turning to FIG. 1, a conventional system 100 can be seen. This system 100 generally comprises a motor controller 102, a power supply 104, an inverter 106, and a motor 108 (which is typically a PMSM or BLDC). In operation, the motor controller 102 provides generally continuous pulse width modulation (PWM) signals (i.e., 6 PWM signals if the motor 108 is a three-phase motor). These PWM signals are used to control the inverter 106, so that the inverter 106 can provide the commanded voltage to each phase of motor 108 from power supply 104.
The motor controller 102 provides control of motor 108 (through the application of the PWM signals) based on a field-oriented control (FOC) algorithm. For conventional FOC control, there are typically three control loops (one speed loop and two current loops) that are employed to provide adjustments. Typically, the observer 120 forms a portion of the speed loop and determines a feedback speed or feedback signal ω from the PWM signals (provided to the inverter 106) and from the motor 108. A difference between this feedback signal ω and a reference speed or reference signal ω* (which is determined by assert 110-1) is adjusted by the proportional-integral (PI) controller 112-1 to generate the reference torque current iq* for the quadrature axis or q-axis. Additionally, a field weakener 114 provides the reference field current id* for the direct axis d-axis (in normal operation, id*=0). The observer 120 also determined the rotor position or angle and provides the angle signal θ to the Park converter 118 and PWM controller 116. The current loops generally includes the Park converter 118, which determines currents id and iq from phase current measurements and the angle signal θ. These currents id and iq are then compared to or subtracted from the reference current id* and iq* by adders 110-2 and 110-3, respectively, to generate errors ΔId and ΔIq. These errors ΔId and ΔIq can then be further adjusted by PI controllers 112-2 and 112-3, and the commanded voltages Vd and Vq, along with the angle signal θ (which form a voltage command vector {right arrow over (V)}), can be used to generate the PWM signals, and generation of the PWM signals is usually accomplished by an inverse Park transformation (performed by an inverse Park converter within PWM controller 116) and a space vector PWM generator (within the PWM controller 116) so as to generate three phase voltages.
There are some drawbacks, however, to using conventional, sensorless FOC controls for PMSMs. Namely, the observer 120 is usually the limiting feature because of computationally intensive processes performed by the observer 120 and because of the complexity of the system 100 with simultaneous current and/or voltage measurements. Usually, there are multiple observers employed (i.e., one for speed/position and one for online parameter estimation), and these observers will oftentimes compete with one another, creating performance degradation, largely because decoupling the observers is difficult. Therefore, it is desirable to have a sensorless FOC-type system with robust performance and a low cost.
Some examples of conventional systems are: U.S. Pat. No. 5,886,498; U.S. Pat. No. 7,202,629; U.S. Pat. No. 7,208,908; U.S. Pat. No. 7,339,344; U.S. Pat. No. 7,646,164; U.S. Pat. No. 7,808,201; U.S. Patent Pre-Grant Publ. No. 2011/0012544; Ancuti et al., “Sensorless V/f control of high-speed surface permanent magnet synchronous motor drives with two novel stabilizing loops for fast dynamics and robustness,” IET Electr. Power Appl., Vol. 4, Iss. 3, 2010, pp. 149-157; Itoh et al., “A comparison between V/f control and position-sensorless vector control for the permanent magnet synchronous motor,” Proc. of the Power Conversion Conf., 2002. PCC Osaka 2002, pg. 1310-1315; and Perera et al., “A Sensorless, Stable V=f Control Method for Permanent-Magnet Synchronous Motor Drives”, IEEE Trans. on Ind. Appl., Vol. 39, No. 3, May/June 2003.